1. Field
This disclosure relates generally to a wireless communication system and, more specifically, to techniques for radio link problem and recovery detection in a wireless communication system.
2. Related Art
As is well known, a wireless channel provides an arbitrary time dispersion, attenuation, and phase shift in a transmitted signal. While the implementation of orthogonal frequency division multiplexing (OFDM) with a cyclic prefix in a wireless communication system mitigates the effect of time dispersion caused by a wireless channel, in order to apply linear modulation schemes it is also usually necessary to remove amplitude and phase shift caused by the wireless channel. Channel estimation is typically implemented in a wireless communication system to provide an estimate (from available pilot information) of an amplitude and phase shift caused by a wireless channel. Equalization may then be employed in the wireless communication system to remove the effect of the wireless channel and facilitate subsequent symbol demodulation. Channel tracking is also usually employed to periodically update an initial channel estimation. For example, channel tracking may be employed to facilitate periodic frequency-domain and time-domain channel correlation and periodic updating of channel signal-to-noise ratio (SNR), channel delay spread, and channel Doppler effect.
Known approaches for detecting a radio link problem (RLP) and a radio link recovery (RLR) in wireless communication systems suffer from significant shortcomings that affect the accuracy and/or testability of a detection approach. Unfortunately, without a good RLP/RLR metric that is both accurate, easily implementable, and testable, wireless communication system performance inevitably degrades. For example, in a third-generation partnership project long-term evolution (3GPP LTE) compliant wireless communication system, user equipment (UE) must be able to accurately detect a radio link problem (RLP) and a radio link recovery (RLR) to prevent performance degradation of the system.
A known first approach for determining an RLP and an RLR at a UE in an LTE compliant wireless communication system has proposed using a physical control format indicator channel (PCFICH) and a pseudo-error rate that is based on received symbols. Unfortunately, the first approach may be inaccurate as there is no clear indication of whether the decoded message is correct due to the absence of an error detection code (e.g., a cyclic redundancy check (CRC)) and the small number of subcarriers associated with the PCFICH (e.g., 16 subcarriers in an LTE system). A known second approach for determining an RLP and an RLR at a UE in an LTE compliant wireless communication system has proposed using a combination of an actual PCFICH and an actual physical downlink control channel (PDCCH) to detect radio link failure. Unfortunately, a UE may not always get a PDCCH grant and, thus, logging a CRC error rate is usually inaccurate as the UE cannot distinguish between a true decoding error and the absence of a PDCCH grant. In addition, the second approach also uses the actual PCFICH which does not have an associated CRC.
A known third approach for determining an RLP and an RLR at a DE in a wireless communication system has proposed using a hypothetical PDCCH transmission to map to an estimate of a block error rate (BLER) as the metric for RLF detection. While overcoming most of the shortcomings in the above-referenced approaches, the third approach still neglects the fact that a successful PCFICH decoding is necessary before a PDCCH can be decoded correctly. As such, the third approach may provide an overly optimistic result, which could be problematic in environments with low signal-to-interference and noise ratios (SINRs) where radio link failure (RLF) is expected to occur. Furthermore, the third approach is not particularly feasible from a conformance testing point of view as a PDCCH error rate is not observable without PCFICH errors. As such, a UE may experience behavior consistency problems when the third approach is employed.